This invention relates to a bell-shaped shield for use on a household appliance, particularly a hand blender or a hand mixer, having a space formed by the inner wall of the shield and accessible from the bottom via an opening through which food is supplied and discharged, a blade-like processing tool inside the space being adapted to be set in rotation by a drive shaft so that the food is caught, comminuted and/or mixed by said tool.
A shield of this type is known from U.S. Pat. No. 3,299,924, for example. The shield continues in upward direction in a sleeve provided with a bore in which a drive shaft is rotatably mounted and carried in bearings so as to be supported axially. The drive shaft extends through the wall of the shield via a bore, projecting with its free end a small amount into the space of the essentially bell-shaped shield. On this free end is a blade-like processing tool for comminuting and mixing or purxc3xa9eing food materials, said processing tool being constructed to extend in a direction transverse to the longitudinal direction of the drive shaft. The other end of the drive shaft is connected by way of a coupling device to an electric motor of a hand mixer. The drive shaft extends concentrically with the sleeve and the shield.
With the hand mixer in operation, food is drawn by the rotary movement of the processing tool through the opening at the free end of the shield, comminuted and, on account of the centrifugal forces generated by the blade, expelled through the slits provided in the wall of the shield. Hence with the appliance activated for a time of some length, the food is returned repeatedly to the processing tool where it is reduced and expelled again out of the shield. As this occurs, it is possible, of course, not only for the food materials to escape to the outside through the slits but also for parts of it to escape over the brim of the opening from where they are then drawn in again centrally by the processing tool. When using the hand blender attachment the food is therefore comminuted, mixed and aerated. The latter occurs when the processing tool rotates at sufficiently high velocity and the suction forces are of a magnitude causing air to be drawn in from the surface. This can also happen, however, when the shield plus drive mechanism is frequently lifted, meaning that it is moved close to the surface of the food and not only held at the bottom of the vessel filled with largely liquid. food. With this mixing device it is difficult to achieve thorough reduction and mixing of the food in a minimum of time because the inside space of the shield is of a more or less rotationally symmetrical configuration.
It is an object of the present invention to provide a shield for a rotary processing tool of a household appliance, particularly an electric hand mixer or a hand blender, with which it is possible to mix, comminute and aerate the food far more intensively in a minimum of time. Furthermore, it is desirable that the shield afford ease of manufacture and cleaning.
This object is accomplished in accordance with the present invention by equipping a shield with bulges on its inner surface the food materials drawn in by the processing tool as the result of the suction forces arising during its rotation are caught and expelled radially outwardly and simultaneously in peripheral direction. According to the invention the food is fed into the bulges, which lie further out radially, as well as against the wall sections. That part of the food which impacts against the wall sections is decelerated there and diverted so that a major part of it is returned to the processing tool where it is reduced and mixed again. A further part of the food gets into the bulges and is moved downward and out through the opening. The result therefore is a continuous mixing, comminuting and aerating cycle.
The bulges have the effect of producing a particularly turbulent flow in the space of the shield, causing the food materials to be intensively mixed and reduced. Large pieces of food are also better caught by the processing tool when they enter the bulges, are trapped there and directed back to the processing tool. Owing to the fact that the food moves in the bulges at a lower speed and may even come to a stand-still there occasionally, also such food materials as project into the bulges in the space between the radial outer edge of the blade and the inner wall of the shield, such as large pieces, can be decelerated to such an extent that, when caught by the processing tool, they are still so sluggish as to be easily cut by the fast running blade. As a result of the bulges the kinetic energy transmitted to the food in the form of radially and peripherally directed movement in addition to the cutting energy from the processing tool also causes pieces of food lying against the inner wall of the shield to be abruptly diverted in their movement. Part of the food materials are even returned to the processing tool and immediately cut again, mixed and conveyed outwards.
As mentioned in the foregoing, the processing tool is preferably a blade having crescent-shaped elements extending radially away from both sides of the drive shaft and equipped with cutting edges on their leading sides as seen in the direction of rotation, said crescent elementsxe2x80x94like a propeller xe2x80x94being twisted and set in such a way as to produce a type of pumping effect causing the food to be drawn in by the processing tool and then expelled radially outwards. The shield forms a certain mixed circuit by which already reduced food as well as food that is still unreduced is fed towards and away from the blade, comminuted and mixed. A large portion of the food is also expelled from the shield radially outwardly allowing new food to enter the space of the shield through the opening when passages are constructed in addition laterally in the wall of the shield.
With the bulges extending in the longitudinal direction of the shield they are readily accessible for cleaning from the opening. The bulges may have a cross section of any desired shape such as angular, tapered, semicircular, oval, etc. It is to be noted, however, that the elevations adjoining each bulge laterally must not extend radially inwards into the blade""s radius of action. According to the invention it could even suffice for just a single clearance space to be constructed on the inner wall of the shield. It is particularly advantageous, however, for several clearance spaces to be spread around the circumference of the inner wall as this generates a particularly turbulent flow in the space of the shield.
In order to be able to hold the shield particularly steady and free from vibrations during the mixing or comminuting operation it is an advantage for the clearance spaces to be spaced evenly apart on the inside of the circumference and to be constructed if possible with the same dimensions. The opening of the shield is preferably always bigger than the biggest diameter of the blade. It will be appreciated that smaller diameters could be selected for the opening but this might have an adverse effect on cleaning and installing the blade in the space of the shield.
Providing bulges that extend in the direction of the drive axis of the shield, taking the shortest route results in a particularly vertical impact of the food against the inner wall of the shield, producing optimal purxc3xa9eing, comminuting and mixing results. A shield of this type is also easy to move back and forth and up and down in a vessel.
In one embodiment, the bulges emerge as elevations on the contour of the envelope surface. In this arrangement the wall of the shield is selected just thick enough for the clearance spaces constructed on the inner side to form elevations on the outer envelope surface. It would also be conceivable, however, for the outer envelope surface to have no elevations, meaning for it to have a smooth surface. In this case the wall of the, shield would have to be selected thick enough for the bulges to be able to penetrate far enough in to the material of the wall.
On a thin-walled shield wherein elevations result between the bulges on the inner wall, the elevations forming in turn constrictions on the envelope surface of the shield, such features result in elevations on the outer surface radially opposite the bulges, while the elevations constructed on the inner side between two clearance spaces become constrictions on the outer envelope surface. A shield of this form is a particularly material-saving, economical, and easy-to-handle solution and is particularly simple to manufacture as a plastic injection-molded part.
In one embodiment, the inner wall of the shield provided with the bulges and the elevations is formed of rings shaped in an undulating or zigzagging configuration in cross section. This arrangement provides for a particularly advantageous shape of the shield wall, with the added effect that the wall extends concentrically with the drive axis. The undulating or zigzagging configuration of the shield wall also extends symmetrically to the drive axis of the shield when looking vertically into the opening of the shield from underneath. It will be understood, of course, that other shapes of wall are also possible, the important thing being that the wall be equipped with groove-shaped, flute-like or stud-type bulges which result in the advantages described above.
In one embodiment, the envelope surface of the shield forms rings shaped in an undulating or zigzagging configuration in cross section, the rings extending concentrically with the inner rings and being congruent therewith. In this arrangement, the outer envelope surface is always equi-distant from the inner wall, i.e., the shield wall is the same thickness in this area all around the circumference.
According to another feature of the invention, the bulges and the constrictions increase in width over their entire length towards the opening. Thus, the clearance spaces increase in depth relative to the shield wall the closer they get to the opening so that mixing, comminuting and the bursting of air bubbles increases towards the opening at the brim. The suction power of the processing tool and the acceleration of the food into the inside of the shield are also greatest in the area of the processing tool, i.e., including the area where the bulges have the deepest profiles.
According to another feature of the invention, the bulges and the constrictions increase in width over their entire length towards the opening. Thus, the width of the bulges on the inner surface and hence the width of the elevations on the outer envelope surface increase towards the opening of the shield, i.e., the shield has a particularly homogenous form. It should be noted at this point that the term xe2x80x9cconstrictionsxe2x80x9d is used for those flutes which an observer recognizes when looking at the surface of the shield from the outside. If the observer looks into the opening vertically from underneath, these constrictions form inwardly extending bulges. Similarly, the adjoining elevations form the bulges on the inner wall.
According to another feature of the invention, the constrictions extending on the envelope surface away from the opening run out in such a way as to end on the envelope surface in the upper end section of the shield. The constrictions in the bell-shaped envelope surface of the shield run out towards the shank because they extend essentially parallel to the drive axis of the shield and the envelope surface of the shield is of a tapering configuration upwards to the drive axis, extending obliquely to the drive axis. The same applies accordingly to another feature of the invention in which the bulges on the inner wall become progressively smaller towards the upper end section, eventually even running out on the inner wall in the upper end so that the inner wall of the shield returns to a circular shape in the upper zone. Here it is thus possible to insert a cap penetrated by the drive shaft to seal off the interior of the shield from the upper space. The upper space is connected to the space of an electric drive mechanism via a bore in which the drive shaft runs. The bore extends in a shank integrally molded to the shield at the end remote from the opening.
Since outer and inner diameter of the shield increases towards the opening it is an advantage for the bulges on the inner side and the constrictions on the envelope surface to also increase in width towards the opening. This enhances the discharge of the food materials in the clearance spaces formed by the bulges.
It is also conceivable, however, for the bulges and the constrictions to be arranged to extend helically at an angle to the drive axis, i.e., either in the opposite or the same direction of rotation as the blade. This has the added effect of enabling the food to be adjusted in its direction of movement either obliquely upwards or obliquely downwards in the longitudinal direction of the bulges, depending in which direction the food impacts against the inner wall of the bulges. It is also possible however for the constrictions to be constructed in the form of stud-like recesses in the wall of the shield extending into the brim of the opening.
According to another feature of the invention, the brim of the shield bounding the opening has not only bulges extending in longitudinal direction along the inner side of the shield but also wave troughs extending along the brim of the shield, the troughs producing passages which also allow part of the food materials to escape radially outwardly from the shield. This is an advantage in particular when the brim of the shield opening rests on the bottom of a vessel because then the food could no longer escape to the outside through the opening closed by the bottom of the vessel but only through the passages.
With an undulating or zigzagging configuration of the shield brim the indentations create a corresponding number of passages through which the food can escape to the outside. These shapes also enable a symmetrical arrangement as is the case with the bulges and the constrictions. The undulating or zigzagging configuration of the brim of the opening coincides in radial direction with the constrictions and elevations, resulting accordingly in a brim zone extending in three planes.
According to another feature of the invention, the wave troughs form the deepest or the furthest projecting points in the longitudinal direction of the shield looking at the shield from the front so that they form a plane which, when placed on the smooth bottom of a vessel, falls in the plane of the bottom. This is achieved structurally by having the end of the brim lie on the inner side of an imaginary conical funnel surface whose apex lies underneath the opening on the drive axis of the recess. Consequently the radially outer zones of the brim, i.e., the walls of the bulges (seen from inside), are intersected earlier than those zones which are radially closer to the drive axis, as is the case with the elevations This results in the lateral passages at the lower brim.
It is also conceivable, however, for the constriction with a wave crest looking from the outside and for the bulge with a wave crest looking from the inside to cooperate with the indentations. This is achieved by having the end of the brim extend along the outer surface of a cone so that the apex of the cone lies advantageously in the area of the recess or in the area of the shield shank on the drive axis. In this case the peaks of the wave troughs of the recess form the front-most end zone while the wave crests of the indentations are recessed. Hence the wave troughs form the support surface of the hand mixer or of the hand blender shank coupled to a household appliance. The passages are then formed by the wave crests. In this configuration, however, the cone angle must not be smaller than that permitted by the curvature of the shield as otherwise the passages will become too big or too much stock will be cut off the shield wall.
A shield wall of constant thickness is achieved by another feature of the invention in which the surface of the inner wall extends so as to be congruent with the envelope surface of the shield.
A particularly homogeneous and enclosed form of the shield with a constant thickness is achieved by another feature of the invention in which the bell-shaped shield extends concentrically with the drive axis and the brim extends symmetrically thereto.